Method of and apparatus for detecting malfunction of displacement detector

Abstract

Displacement detector includes a displaceable core, two detecting coils variable in their inductance in response to displacement of the core, and two reference resistances each connected in series with the corresponding detecting coil. Pulse power is supplied to each pair of the series-connected detecting coil and reference resistance, and two transient response voltages across the reference resistances are taken out. Two bottom holding circuits are also provided in corresponding relation to transient response voltages, so that each of the bottom holding circuits detects and holds a smallest or bottom level of the corresponding transient response voltage and thereby provides the bottom voltage as an output voltage. Then, a difference is evaluated between the two output voltages from the bottom holding circuits. When the difference between the two output voltages is below a predetermined value, the displacement detector is determined as malfunctioning due to a short-circuit state between the transient response voltages.

What is claimed is: 
     
       1. A method of detecting a malfunction of a displacement detector, said displacement detector including a displaceable core, two detecting coils variable in inductance in response to displacement of the core and two converters for converting variations of the inductance of the two detecting coils into variations of voltage and being arranged to prevent output voltages of the two detecting coils from coinciding with each other over a normal operating range of said displacement detector, said method comprising the steps of: evaluating a difference between output voltages from said converters; and   determining said displacement detector as malfunctioning due to a short-circuit state occurring between the output voltages of the detecting coils, when an absolute value of the difference between output voltages is below a predetermined value.   
     
     
       2. A method as recited in claim 1 wherein said displacement detector is a torque detector that includes an input shaft, an output shaft, and a torsion bar interconnecting the input and output shafts, and wherein the core of said torque detector engages with said input and output shafts and is displaceable in response to steering torque acting on said input and output shafts. 
     
     
       3. A method as recited in claim 1 wherein said displacement detector further includes two reference resistances each connected in series with a corresponding one of said detecting coils, and a pulse power supply for supplying pulse power to each pair of the detecting coil and the reference resistance connected in series, and wherein said displacement detector detects a transient response voltage across each of said reference resistances. 
     
     
       4. A method as recited in claim 1 wherein said displacement detector further includes two reference resistances each connected in series with a corresponding one of said detecting coils, said two reference resistances and said two detecting coils being connected to form a bridge circuit, and a pulse power supply for supplying pulse power to said bridge circuit, and wherein said displacement detector detects a transient response voltage across each of said reference resistances. 
     
     
       5. An apparatus for detecting a malfunction of a displacement detector, said displacement detector including a displaceable core, two detecting coils variable in inductance in response to displacement of the core and two converters for converting variations of the inductance of the two detecting coils into variations of voltage and being arranged to prevent output voltages of the two detecting coils from coinciding with each other over a normal operating range of said displacement detector, said apparatus comprising: a section for evaluating a difference between output voltages from said converters; and   a section for determining said displacement detector as malfunctioning due to a short-circuit state occurring between the output voltages of the detecting coils, when an absolute value of the difference between output voltages is below a predetermined value.